ITMI20091768A1 - PROCESS FOR LNG PLANTS ALSO WITH LARGE CAPACITY ASKING FOR LOW VOLUMETRIC REACHES TO REFRIGERATING COMPRESSORS - Google Patents
PROCESS FOR LNG PLANTS ALSO WITH LARGE CAPACITY ASKING FOR LOW VOLUMETRIC REACHES TO REFRIGERATING COMPRESSORS Download PDFInfo
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- ITMI20091768A1 ITMI20091768A1 IT001768A ITMI20091768A ITMI20091768A1 IT MI20091768 A1 ITMI20091768 A1 IT MI20091768A1 IT 001768 A IT001768 A IT 001768A IT MI20091768 A ITMI20091768 A IT MI20091768A IT MI20091768 A1 ITMI20091768 A1 IT MI20091768A1
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- exchanger
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- natural gas
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- 238000000034 method Methods 0.000 title claims description 32
- 239000003507 refrigerant Substances 0.000 claims description 82
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 67
- 239000007788 liquid Substances 0.000 claims description 34
- 238000007906 compression Methods 0.000 claims description 31
- 239000003345 natural gas Substances 0.000 claims description 28
- 230000006835 compression Effects 0.000 claims description 25
- 239000000203 mixture Substances 0.000 claims description 20
- 238000005057 refrigeration Methods 0.000 claims description 16
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 claims description 10
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 claims description 6
- 238000009833 condensation Methods 0.000 claims description 5
- 230000005494 condensation Effects 0.000 claims description 5
- 235000013844 butane Nutrition 0.000 claims description 4
- 239000012530 fluid Substances 0.000 claims description 4
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical class CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 3
- 125000000383 tetramethylene group Chemical group [H]C([H])([*:1])C([H])([H])C([H])([H])C([H])([H])[*:2] 0.000 claims description 2
- 238000001816 cooling Methods 0.000 claims 2
- 238000013021 overheating Methods 0.000 claims 1
- 238000009834 vaporization Methods 0.000 claims 1
- 230000008016 vaporization Effects 0.000 claims 1
- 239000007789 gas Substances 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000001704 evaporation Methods 0.000 description 4
- 238000011084 recovery Methods 0.000 description 4
- 239000001294 propane Substances 0.000 description 3
- 239000002826 coolant Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000008020 evaporation Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 238000009835 boiling Methods 0.000 description 1
- 239000001273 butane Substances 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 239000000567 combustion gas Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- PPASLZSBLFJQEF-RKJRWTFHSA-M sodium ascorbate Substances [Na+].OC[C@@H](O)[C@H]1OC(=O)C(O)=C1[O-] PPASLZSBLFJQEF-RKJRWTFHSA-M 0.000 description 1
- 239000012808 vapor phase Substances 0.000 description 1
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
- F25J1/0292—Refrigerant compression by cold or cryogenic suction of the refrigerant gas
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
- F25J1/0022—Hydrocarbons, e.g. natural gas
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
- F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
- F25J1/004—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by flash gas recovery
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
- F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
- F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
- F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
- F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
- F25J1/0055—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream originating from an incorporated cascade
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0211—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle
- F25J1/0214—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
- F25J1/0291—Refrigerant compression by combined gas compression and liquid pumping
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2220/00—Processes or apparatus involving steps for the removal of impurities
- F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
- F25J2220/62—Separating low boiling components, e.g. He, H2, N2, Air
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
- F25J2290/12—Particular process parameters like pressure, temperature, ratios
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Separation By Low-Temperature Treatments (AREA)
- Filling Or Discharging Of Gas Storage Vessels (AREA)
Description
DESCRIZIONE DI INVENZIONE INDUSTRIALE DESCRIPTION OF INDUSTRIAL INVENTION
PROCESSO PER IMPIANTI GNL ANCHE DI GRANDE CAPACITA' RICHIEDENTE BASSE PORTATE VOLUMETRICHE Al COMPRESSORI FRIGORIFERI, PROCESS FOR LNG PLANTS ALSO OF LARGE CAPACITY REQUIRING LOW VOLUMETRIC FLOW RATES TO THE REFRIGERATING COMPRESSORS,
Introduzione: Introduction:
L'industria del GNL è stata segnata fin dall’inizio dalla necessità di ridurre i costi, cui si è risposto ricorrendo principalmente all’economia di scala. La tendenza a linee di liquefazione di maggiore capacità è stata sempre limitata dalla capacità delle apparecchiature disponibili, in particolare compressori e motrici. L'industria meccanica ed elettromeccanica ha reso disponibili macchinari di crescente potenza, dando il maggior contributo all’aumento della produzione della singola linea di liquefazione. Anche la tecnologia del GNL si è costantemente evoluta, cercando: The LNG industry was marked from the beginning by the need to reduce costs, which was responded to by resorting mainly to the economy of scale. The trend towards higher capacity liquefaction lines has always been limited by the capacity of available equipment, in particular compressors and engines. The mechanical and electromechanical industry has made machinery of increasing power available, making the greatest contribution to the increase in production of the single liquefaction line. LNG technology has also constantly evolved, seeking:
- di diminuire l'energia specifica di liquefazione per ottenere il massimo di produzione dal macchinario esistente - to decrease the specific liquefaction energy to obtain the maximum production from the existing machinery
- di ripartire in misura opportuna la potenza totale tra i cicli frigoriferi del processo per poter impiegare in ciascuno di essi il macchinario della massima capacità. In questi campi la tecnica nota ha ottenuto notevoli successi, proponendo schemi di liquefazione a basso consumo energetico e sufficientemente flessibili. - to appropriately divide the total power between the refrigeration cycles of the process in order to use the machinery of maximum capacity in each of them. In these fields, the known art has achieved considerable successes, proposing liquefaction schemes with low energy consumption and sufficiently flexible.
Rispettando i predetti risultati, la presente invenzione porta un contributo all’aumento della capacità della singola linea di liquefazione. Gli schemi proposti consentono una sostanziale riduzione della portata volumetrica dei compressori frigoriferi, senza diminuirne le prestazioni. Le dimensioni dei compressori risultano minori. Ne conseguono due importanti risultati: By respecting the aforementioned results, the present invention makes a contribution to increasing the capacity of the single liquefaction line. The proposed schemes allow a substantial reduction in the volumetric flow rate of the refrigeration compressors, without reducing their performance. The dimensions of the compressors are smaller. Two important results follow:
- in molti casi il costo dei compressori è inferiore - in many cases the cost of the compressors is lower
- soprattutto, è possibile a parità di portata volumetrica ottenere dal compressore una maggior potenza di refrigerazione, e quindi costruire linee di maggiore capacità. - above all, with the same volumetric flow rate it is possible to obtain a greater refrigeration power from the compressor, and therefore to build lines of greater capacity.
Descrizione. Description.
Alcuni dei criteri che vengono proposti possono essere utilizzati in ogni ciclo frigorifero a refrigerante misto, tuttavia nel seguito per concretezza viene descritta la loro applicazione ad un processo a due cicli frigoriferi. La refrigerazione necessaria viene prodotta da un ciclo, nel seguito detto primario, che liquefa e sottoraffredda il gas naturale, e da un altro ciclo, detto secondario, che preraffredda il gas naturale e condensa il refrigerante del ciclo primario. Questi cicli possono essere suddivisi in più stadi di refrigerazione-compressione, nel seguito indicheremo come primo lo stadio a minor pressione. Anche se in ogni stadio possono essere presenti alcune apparecchiature ausiliarie, in questa descrizione di principio si tratterà principalmente dello scambiatore, in cui le correnti di processo vengono raffreddate e/o condensate evaporando il refrigerante, e dello stadio di compressione, che comprime il refrigerante evaporato fino alla pressione dello stadio successivo o dello stadio finale. In particolare, come è usuale pratica della tecnica nota, le correnti di refrigerante vengono sottoraffreddate prima dell’espansione per ottenere temperature un poco inferiori. Some of the criteria that are proposed can be used in each refrigerant cycle with mixed refrigerant, however in the following for concreteness their application to a process with two refrigeration cycles is described. The necessary refrigeration is produced by a cycle, hereinafter called primary, which liquefies and subcools the natural gas, and by another cycle, called secondary, which pre-cools the natural gas and condenses the refrigerant of the primary cycle. These cycles can be divided into several refrigeration-compression stages, in the following we will indicate the lower pressure stage as the first. Although some auxiliary equipment may be present in each stage, in this principle description it will mainly deal with the exchanger, in which the process streams are cooled and / or condensed by evaporating the refrigerant, and the compression stage, which compresses the evaporated refrigerant. until the next stage or final stage is pressed. In particular, as is the usual practice of the known art, the refrigerant streams are subcooled before expansion to obtain slightly lower temperatures.
La presente invenzione ha per oggetto un ciclo di liquefazione di gas bassobollenti ed in particolare del gas naturale ad elevata efficienza, e che consente una più elevata capacità. L’invenzione è caratterizzata essenzialmente dal suo ciclo primario, in cui due refrigeranti di composizione diversa vengono alimentati ai due stadi del ciclo, e dal suo ciclo secondario, nel quale il refrigerante non viene completa mente vaporizzato nei rispettivi scambiatori, separando all’uscita una fase di vapore saturo che viene direttamente alimentato al compressore, ed una fase liquida che viene utilizzata in un punto diverso deirimpianto. The present invention relates to a liquefaction cycle of low-boiling gases and in particular of natural gas with high efficiency, and which allows a higher capacity. The invention is essentially characterized by its primary cycle, in which two refrigerants of different composition are fed to the two stages of the cycle, and by its secondary cycle, in which the refrigerant is not completely vaporized in the respective exchangers, separating a saturated vapor phase which is directly fed to the compressor, and a liquid phase which is used in a different point of the system.
Il processo complessivo di liquefazione del gas naturale è illustrato nell'esempio che segue con riferimento alle figure 1 , 2 e 3. The overall process of liquefaction of natural gas is illustrated in the following example with reference to Figures 1, 2 and 3.
Ciclo primario. E’ noto che per diminuire la portata volumetrica max. a un ciclo frigorifero è possibile suddividere il ciclo in due o più stadi: le portate volumetriche a ciascun stadio sono inferiori rispetto alla portata che si avrebbe con un ciclo ad un solo stadio. Questo schema è stato applicato dalla tecnica nota ad un ciclo a due stadi di refrigerazione-compressione mantenendo immutata la composizione del refrigerante in tutto il ciclo, e quindi anche nelle alimentazioni ai due scambiatori del ciclo. Secondo questo schema la composizione del refrigerante deve essere sufficientemente leggera da evaporare completamente alle condizioni di uscita dello scambiatore di secondo stadio. Di conseguenza, nello scambiatore di primo stadio dove la pressione è minore il refrigerante evapora completamente ben prima dell’uscita dallo scambiatore ed esce da esso significativamente surriscaldato. Le calorie per grado acquistate durante il surriscaldamento (calore sensibile) sono inferiori a quelle acquistate durante l’evaporazione (calore latente), per cui le calorie totali acquistate dal refrigerante nel primo scambiatore sono significativamente inferiori a quelle che sarebbero acquistate se il fluido nello scambiatore acquistasse calorie solo per evaporazione, cioè se la sua composizione fosse più pesante. La suddivisione del ciclo in due stadi secondo questo schema comporta una elevata portata di refrigerante di primo stadio - anche se inferiore a quella di un ciclo a un solo stadio -e in totale una maggior potenza del ciclo. Variazioni a questo schema di suddivisione finora pubblicate non comportano particolari vantaggi (Gazzi e Sguera brev. it. Primary cycle. It is known that to decrease the max. in a refrigeration cycle it is possible to divide the cycle into two or more stages: the volumetric flow rates at each stage are lower than the flow rate that would occur with a single stage cycle. This scheme has been applied by the known art to a two-stage refrigeration-compression cycle while maintaining the composition of the refrigerant unchanged throughout the cycle, and therefore also in the feeds to the two exchangers of the cycle. According to this scheme, the composition of the refrigerant must be light enough to evaporate completely at the outlet conditions of the second stage exchanger. Consequently, in the first stage exchanger where the pressure is lower, the refrigerant evaporates completely well before it leaves the exchanger and leaves it significantly overheated. The calories per degree acquired during superheating (sensible heat) are lower than those acquired during evaporation (latent heat), so the total calories purchased by the refrigerant in the first exchanger are significantly lower than those that would be purchased if the fluid in the exchanger acquired calories only by evaporation, that is, if its composition was heavier. The division of the cycle into two stages according to this scheme involves a high flow rate of the first stage refrigerant - even if lower than that of a single stage cycle - and in total a greater power of the cycle. Variations to this subdivision scheme published so far do not involve particular advantages (Gazzi and Sguera brev. It.
1 176290, Paradowski e Rojey Usa pat 6105389). A risparmio di potenza la tecnica nota usa perciò un ciclo primario a un solo stadio (Martin, Pigourier e Boutelant: Liquefin, an innovative process to reduce LNG costs, 22th Word Gas Conference, Tokio, 2003). 1 176290, Paradowski and Rojey Usa pat 6105389). In power saving, the known technique therefore uses a single-stage primary cycle (Martin, Pigourier and Boutelant: Liquefin, an innovative process to reduce LNG costs, 22th Word Gas Conference, Tokyo, 2003).
Nello schema qui proposto il ciclo primario è previsto in due stadi, e in essi vengono evaporati refrigeranti aventi diversa composizione. Ci sono diversi modi per ottenere composizioni diverse. Il refrigerante del ciclo può essere alimentato tal quale ai due stadi, ma nel secondo scambiatore, che è a pressione più alta, ne viene evaporata solo la parte più leggera, avviata al secondo stadio di compressione, mentre il liquido residuo viene espanso alla pressione di primo stadio. Nello scambiatore di primo stadio il refrigerante viene parzialmente evaporato, poi in uscita dallo scambiatore viene appesantito unendovi il liquido residuo dallo scambiatore di secondo stadio. La miscela viene completamente evaporata nello scambiatore di secondo stadio, da cui esce a temperatura di poco superiore al suo punto di rugiada, e viene avviata al primo stadio di compressione. In questo modo entrambi gli scambiatori vengono raffreddati con calore latente e non con calore sensibile, le portate dei due stadi sono minimizzate. In the scheme proposed here, the primary cycle is foreseen in two stages, and refrigerants having different compositions are evaporated in them. There are several ways to get different compositions. The refrigerant of the cycle can be fed as it is to the two stages, but in the second exchanger, which is at a higher pressure, only the lighter part is evaporated, sent to the second compression stage, while the residual liquid is expanded at the pressure of first stage. In the first stage exchanger, the refrigerant is partially evaporated, then at the outlet of the exchanger it is heavier by joining the residual liquid from the second stage exchanger. The mixture is completely evaporated in the second stage exchanger, from which it comes out at a temperature just above its dew point, and is sent to the first compression stage. In this way both exchangers are cooled with latent heat and not with sensible heat, the flow rates of the two stages are minimized.
Uno schema più flessibile, che consente di meglio definire le composizioni secondo le necessità del ciclo, consiste nel separare un liquido ed un vapore ad una opportuna temperatura durante la condensazione del refrigerante primario, e poi condensare e sottoraffreddare il vapore nel ciclo primario rievaporandolo in parte nello scambiatore di primo stadio. In questo modo il refrigerante di primo stadio è più leggero e produce più facilmente la bassa temperatura richiesta dal processo. Il liquido viene alimentato al secondo scambiatore e parzialmente vaporizzato. Il vapore viene avviato al secondo stadio di compressione, il liquido residuo viene espanso alla pressione di primo stadio, miscelato al refrigerante in uscita dal primo scambiatore, che risulta appesantito, ed alimentato come nello schema precedente al secondo scambiatore. A more flexible scheme, which allows to better define the compositions according to the needs of the cycle, consists in separating a liquid and a vapor at a suitable temperature during the condensation of the primary refrigerant, and then condensing and subcooling the vapor in the primary cycle by re-evaporating it in part. in the first stage exchanger. In this way the first stage coolant is lighter and more easily produces the low temperature required by the process. The liquid is fed to the second exchanger and partially vaporized. The vapor is sent to the second compression stage, the residual liquid is expanded at the first stage pressure, mixed with the refrigerant leaving the first exchanger, which is heavier, and fed to the second exchanger as in the previous diagram.
Può essere talvolta opportuno utilizzare nel primo scambiatore un refrigerante sempre più leggero del refrigerante totale del ciclo, ma più pesante del vapore ottenuto durante la condensazione parziale. In questo caso si può condensare il vapore ed aggiungervi una parte del liquido separato durante la condensazione del refrigerante totale. It may sometimes be advisable to use in the first exchanger a refrigerant that is always lighter than the total refrigerant of the cycle, but heavier than the vapor obtained during partial condensation. In this case, the vapor can be condensed and a part of the separated liquid added to it during condensation of the total refrigerant.
E’ importante notare che sempre il refrigerante dello stadio a bassa pressione è leggero nel primo scambiatore, dove occorre raggiungere le temperature più basse, e poi viene appesantito prima di alimentare il secondo scambiatore, in modo da raffreddare con il calore latente e non con il calore sensibile. It is important to note that the refrigerant of the low pressure stage is always light in the first exchanger, where it is necessary to reach the lowest temperatures, and then it is weighed down before feeding the second exchanger, so as to cool with the latent heat and not with the sensible heat.
Gli schemi precedenti consentono molta flessibilità nella progettazione del ciclo primario. Possono essere ulteriormente variati per adeguarsi ad eventuali richieste del costruttore del compressore. The previous schemes allow a lot of flexibility in the design of the primary cycle. They can be further changed to adapt to any requests from the compressor manufacturer.
Per il refrigerante totale del ciclo primario, dal quale si ottengono i due refrigeranti di diversa composizione, è prevista una composizione molare compresa entro i seguenti limiti: For the total refrigerant of the primary cycle, from which the two refrigerants of different composition are obtained, a molar composition comprised within the following limits is envisaged:
N2 4 - 15 % N2 4 - 15%
CH4 35 - 65 % CH4 35 - 65%
C2H6 e/o C2H4 30 - 48 % C2H6 and / or C2H4 30 - 48%
C3H8 e/o C3H6 0 - 8 % C3H8 and / or C3H6 0 - 8%
Il compressore del ciclo primario opera tra una pressione di aspirazione al primo stadio compresa tra 200 e 500 kPa ed una pressione di mandata compresa tra 3000 e 6500 kPa. The primary cycle compressor operates between a first stage suction pressure between 200 and 500 kPa and a discharge pressure between 3000 and 6500 kPa.
Ciclo secondario. Questo ciclo viene solitamente progettato in più stadi, da tre a cinque, la massima portata volumetrica si ha al primo o al secondo stadio. Si è visto nella descrizione del ciclo primario che se il refrigerante esce dallo scambiatore al suo punto di rugiada, senza essere surriscaldato, la portata necessaria di refrigerante e la potenza del corrispondente stadio di compressione sono minori. Questo criterio può essere applicato anche nel ciclo secondario. Ovviamente non è possibile ottenere che tutti i refrigeranti escano dai rispettivi scambiatori al punto di rugiada, durante la marcia normale e soprattutto nei transitori. La presente invenzione prevede che il refrigerante esca non completamente vaporizzato ed il vapore venga separato ed alimentato al compressore. Il liquido residuo, che in marcia normale e nella maggior parte degli stadi può variare da 0 a 10 % del refrigerante totale alimentato a quello stadio, può essere pompato ed utilizzato in vari modi, alcuni dei possibili sono: - unire il liquido al refrigerante in ingresso allo scambiatore a pressione immediatamente superiore Secondary cycle. This cycle is usually designed in several stages, from three to five, the maximum volumetric flow rate occurs at the first or second stage. It has been seen in the description of the primary cycle that if the refrigerant leaves the exchanger at its dew point, without being overheated, the required refrigerant flow rate and the power of the corresponding compression stage are lower. This criterion can also be applied in the secondary cycle. Obviously it is not possible to obtain that all the refrigerants leave the respective exchangers at the dew point, during normal operation and especially in transients. The present invention provides that the refrigerant is not completely vaporized and the vapor is separated and fed to the compressor. The residual liquid, which in normal operation and in most stages can vary from 0 to 10% of the total refrigerant fed to that stage, can be pumped and used in various ways, some of the possible ones are: - add the liquid to the refrigerant in inlet to the exchanger at immediately higher pressure
- unire il liquido al refrigerante in uscita dallo scambiatore a pressione immediatamente superiore, prima del separatore all’ingresso compressore - add the liquid to the refrigerant leaving the exchanger at the immediately higher pressure, before the separator at the compressor inlet
- unire il liquido al refrigerante totale prima del condensatore o del primo condensatore - add the liquid to the total refrigerant before the condenser or the first condenser
- iniettare i liquidi in almeno uno stadio del compressore. - inject liquids into at least one stage of the compressor.
Le pompe per il recupero dei liquidi aH’uscita degli scambiatori hanno una potenza trascurabile, devono però essere surdimensionate per i casi di emergenza. The pumps for the recovery of liquids at the outlet of the exchangers have a negligible power, however they must be oversized for emergencies.
Il refrigerante secondario ha un maggior peso molecolare medio ed un volatilità minore del primario. La sua composizione molare in uscita dal treno di compressione è compresa entro i seguenti limiti: The secondary refrigerant has a higher average molecular weight and a lower volatility than the primary. Its molar composition leaving the compression train is within the following limits:
CH4 0 - 3 % CH4 0 - 3%
C2H6 e/o C2H4 40 - 70 % C2H6 and / or C2H4 40 - 70%
C3H8 e/o C3H6 35 - 65% C3H8 and / or C3H6 35 - 65%
Butani e/o buteni 0 - 8 % Butanes and / or butenes 0 - 8%
Il treno di compressione del ciclo secondario opera tra una pressione di aspirazione compresa tra 130 e 350 kPa ed una pressione di mandata compresa tra 3000 e 5000 kPa. The compression train of the secondary cycle operates between a suction pressure between 130 and 350 kPa and a delivery pressure between 3000 and 5000 kPa.
Per rendere evidenti le caratteristiche ed i vantaggi del processo secondo l’invenzione si illustra qui di seguito un esempio di realizzazione per la produzione di GNL, con riferimento alle figure 1 , 2 e 3. To highlight the characteristics and advantages of the process according to the invention, an example of implementation for the production of LNG is illustrated below, with reference to Figures 1, 2 and 3.
Esempio. Example.
Il calcolo è stato eseguito con il programma Hysys versione 7.1 , nel seguito le correnti sono state indicate riportando tra parentesi i numeri loro attribuiti nello schema di processo. E’ stata assunta una temperatura dell'acqua di raffreddamento di 28 °C, ed un approccio lato freddo dei refrigeranti ad acqua di 7 °C. I compressori sono stati calcolati con un rendimento politropico di 0,82. Gli scambiatori del ciclo primario hanno una LMTD di 3,5 °C, quelli del ciclo secondario di 5 °C. Le pressioni sono assolute. The calculation was performed with the Hysys version 7.1 program, in the following the currents have been indicated by reporting in brackets the numbers attributed to them in the process diagram. A cooling water temperature of 28 ° C was assumed, and a cold side approach of the water coolants of 7 ° C. The compressors were calculated with a polytropic efficiency of 0.82. The primary cycle exchangers have an LMTD of 3.5 ° C, those of the secondary cycle 5 ° C. The pressures are absolute.
Gas naturale. (Fig. 1) Il gas naturale (100) viene raffreddato a - 62 °C con il ciclo secondario, completamente condensato e sottorafffeddato a - 151 ,54 °C (103) con il ciclo primario, espanso a 150 kPa e poi in serbatoio (109) alla temperatura di - 160,30 °C. Vengono prodotte 961 ,296 ton/h di GNL pari a 8 milioni di ton/anno. L’8% del gas in ingresso, prodotto durante le espansioni del gas liquefatto, costituisce il combustibile per le necessità del processo e dei servizi vari del centro di liquefazione. Dopo recupero frigorie questo gas viene compresso ed alimentato alla rete fuel. Nella seguente tabella è riportato il bilancio materiali globale. Natural gas. (Fig. 1) Natural gas (100) is cooled to - 62 ° C with the secondary cycle, completely condensed and subcooled to - 151, 54 ° C (103) with the primary cycle, expanded to 150 kPa and then in the tank (109) at a temperature of - 160.30 ° C. 961, 296 tons / h of LNG are produced, equal to 8 million tons / year. 8% of the incoming gas, produced during the expansions of liquefied gas, constitutes the fuel for the needs of the process and various services of the liquefaction center. After refrigeration recovery, this gas is compressed and fed to the fuel network. The following table shows the overall material balance.
Gas grezzo GNL Gas combust. Raw gas LNG Combustion gas
Corrente (100) (109) (112) kmol/h 58168,88 53515,34 4653,54 Current (100) (109) (112) kmol / h 58 168.88 53 515.34 4653.54
P, kPa 5700 135 P, kPa 5700 135
T, °C 35 -160,30 -41 T, ° C 35 -160.30 -41
fr. mol., N2 0,00500 0,00122 0,04842 fr. mol., N2 0.00500 0.00122 0.04842
C1 0,09080 0,90422 0,95143 C1 0.09080 0.90422 0.95143
C2 0,05700 0,06194 0,00015 C2 0.05700 0.06194 0.00015
C3 0,02200 0,02391 0,00000 C3 0.02200 0.02391 0.00000
iC4 0,00300 0,00326 0,00000 iC4 0.00300 0.00326 0.00000
nC4 0,00500 0,00543 0,00000 nC4 0.00500 0.00543 0.00000
P. M. 17,856 17,963 16,625 P. M. 17,856 17,963 16,625
Ciclo primario. (Fig. 2) Il ciclo è suddiviso in due stadi, il secondo scambiatore LNG202 raffredda le correnti di processo a - 130 °C, il primo LNG201 a -151,54 °C. Il gas naturale (101) ed il refrigerante primario (220) vengono raffreddati e parzialmente condensati a - 62 °C con il ciclo secondario. Il refrigerante primario entra nel ciclo a - 62 °C e 4800 kPa, parzialmente vaporizzato. Il vapore (209) viene condensato e sottoraffreddato assieme al liquido (203) a -130 °C nel secondo scambiatore ed addizionato di una parte del liquido. La miscela (201 ), che costituisce il refrigerante di primo stadio, viene sottorafffeddata (214) a - 151,54 °C, espansa a 400 kPa e parzialmente evaporata nel primo scambiatore. La maggior parte del liquido (210) viene espansa a 800 kPa e riscaldata fino a - 64 °C e parzialmente evaporata nel secondo scambiatore. Il vapore (218) va al recupero termico in E204 fino a 7 °C e poi al secondo stadio di compressione. Il liquido (219) viene nuovamente sottoraffreddato a -130 °C, espanso alla pressione di primo stadio e unito al refrigerante in uscita dal primo scambiatore (207). La miscela risultante (222) viene evaporata nel secondo scambiatore LNG202 di cui completa la refrigerazione, cede il suo calore sensibile in E205 fino a - 41 °C, poi viene compressa nel primo stadio di compressione e si unisce alla corrente (233) uscente dal recupero termico a 7 °C. Il refrigerante totale (232) viene compresso in ulteriori 3 stadi fino a 4920 kPa, raffreddato con acqua e refrigerante secondario a - 62 °C, e ritorna in ciclo (220). Primary cycle. (Fig. 2) The cycle is divided into two stages, the second exchanger LNG202 cools the process streams to - 130 ° C, the first LNG201 to -151.54 ° C. Natural gas (101) and primary refrigerant (220) are cooled and partially condensed to - 62 ° C with the secondary cycle. The primary refrigerant enters the cycle at - 62 ° C and 4800 kPa, partially vaporized. The vapor (209) is condensed and subcooled together with the liquid (203) at -130 ° C in the second exchanger and a part of the liquid is added. The mixture (201), which constitutes the first stage refrigerant, is subcooled (214) to - 151.54 ° C, expanded to 400 kPa and partially evaporated in the first exchanger. Most of the liquid (210) is expanded to 800 kPa and heated to - 64 ° C and partially evaporated in the second exchanger. The vapor (218) goes to the thermal recovery in E204 up to 7 ° C and then to the second compression stage. The liquid (219) is again subcooled to -130 ° C, expanded to the first stage pressure and combined with the refrigerant leaving the first exchanger (207). The resulting mixture (222) is evaporated in the second exchanger LNG202 of which it completes the refrigeration, releases its sensible heat in E205 down to - 41 ° C, then is compressed in the first compression stage and joins the current (233) leaving the heat recovery at 7 ° C. The total refrigerant (232) is compressed in further 3 stages up to 4920 kPa, cooled with water and secondary refrigerant to - 62 ° C, and returns to cycle (220).
Secondo questo schema dal refrigerante totale vengono prodotte tre correnti, una per raffreddare il primo scambiatore e due per raffreddare il secondo scambiatore. Nella tabella seguente riportiamo le dette correnti alle condizioni di ingresso scambiatore. According to this scheme, three streams are produced from the total refrigerant, one to cool the first exchanger and two to cool the second exchanger. The following table shows the said currents at the exchanger inlet conditions.
Refrigerante Totale 1° scamb. 2° scamb. BP 2° scamb. AP Corrente (220) (215) (222) (205) kmol/h 61834,85 27182,08 33706,21 34652,77 P, kPa 4800 400 390 800 Total refrigerant 1st exchange 2nd exchange BP 2nd exchange AP Current (220) (215) (222) (205) kmol / h 61834.85 27182.08 33706.21 34652.77 P, kPa 4800 400 390 800
T, °C - 62 - 157,66 -130,79 -131 ,46 T, ° C - 62 - 157.66 -130.79 -131.46
fr. mol., N2 0,09141 0,13634 0,11029 0,05617 fr. mol., N2 0.09141 0.13634 0.11029 0.05617
C1 0,50946 0,55770 0,46477 0,47162 C1 0.50946 0.55770 0.46477 0.47162
C2 0,37455 0,28853 0,38628 0,44202 C2 0.37455 0.28853 0.38628 0.44202
C3 0,02458 0,01742 0,03866 0,03019 C3 0.02458 0.01742 0.03866 0.03019
P. M. 23,080 22,21 1 23,866 23,762 P. M. 23,080 22,21 1 23,866 23,762
compressore primario ha le seguenti caratteristiche: primary compressor has the following characteristics:
Stadio P asp., kPa Potenza, kW Portata, mc/h 1 375 17185 167790 Stage P asp., KPa Power, kW Flow rate, mc / h 1 375 17185 167790
2 780 46061 177325 2 780 46061 177325
3° 1840 26976 80337 3 ° 1840 26976 80337
4° 3000 25582 47079 Totale 115784 4 ° 3000 25582 47079 Total 115 784
Ciclo secondario. (Fig. 3) Viene qui descritto il caso in cui il ciclo frigorifero ha quattro stadi. Il refrigerante totale (342) viene condensato in E301 a 3202 kPa e 35 °C. Il liquido (305) viene raffreddato a 10 °C nello scambiatore LNG304 assieme al gas naturale (100) ed al refrigerante primario (240), una parte (309) viene espansa (337), alimentata in controcorrente a LNG304, totalmente vaporizzata ed alimentata (352) al compressore. La parte residua viene raffreddata a - 18,20 °C (313) in LNG303, in cui si ripete lo schema di trattamento dello scambiatore precedente, ma con la differenza che in uscita da LNG303 il refrigerante (317) è vaporizzato per il 98,55 %. Il vapore (328) è avviato alla compressione, il liquido (332) è ripreso con la pompa P303 ed unito al refrigerante (337) in ingresso a LNG304. In uscita da LNG303 il refrigerante residuo (326) viene raffreddato a - 38 °C, espanso, unito alla corrente (304) e vaporizzato in LNG302 per il 97,93 %. Il vapore (323) viene avviato alla compressione, il liquido (324) viene unito al refrigerante (327) all’ingresso di LNG303. Il refrigerante residuo (314) viene sottoraffreddato a - 62 °C, espanso e vaporizzato in LNG301 per il 95,18 %. Il vapore (302) viene avviato alla compressione, il liquido (303) viene miscelato al refrigerante (322) in alimentazione a LNG302. Secondary cycle. (Fig. 3) The case in which the refrigeration cycle has four stages is described here. The total refrigerant (342) is condensed in E301 at 3202 kPa and 35 ° C. The liquid (305) is cooled to 10 ° C in the LNG304 exchanger together with the natural gas (100) and the primary refrigerant (240), a part (309) is expanded (337), fed in counter-current to LNG304, totally vaporized and fed (352) to the compressor. The residual part is cooled to - 18.20 ° C (313) in LNG303, in which the treatment scheme of the previous exchanger is repeated, but with the difference that at the outlet of LNG303 the refrigerant (317) is vaporized for 98, 55%. The vapor (328) is sent to compression, the liquid (332) is taken up with the P303 pump and combined with the refrigerant (337) entering the LNG304. Leaving LNG303 the residual refrigerant (326) is cooled to - 38 ° C, expanded, combined with the stream (304) and vaporized in LNG302 for 97.93%. The vapor (323) is sent to compression, the liquid (324) is combined with the refrigerant (327) at the inlet of LNG303. The residual refrigerant (314) is subcooled to - 62 ° C, expanded and vaporized in LNG301 for 95.18%. The vapor (302) is sent to compression, the liquid (303) is mixed with the refrigerant (322) feeding to LNG302.
Il refrigerante di questo esempio (305) è costituito da etano 60 % e propano 40 % mol, P. M. 35,681. I piccoli quantitativi di metano e di butani che sempre si trovano rispettivamente neN'etano e nel propano prodotti per il rabbocco dei cicli frigo riferì non modificano il comportamento del refrigerante. Metano e butani possono però essere costituenti necessari fino ad un massimo rispettivamente del 3 e 8 % molare in funzione della temperatura ottenibile per la condensazione dei refrigeranti e della temperatura al confine tra i due cicli. The refrigerant of this example (305) consists of 60% ethane and 40% mol propane, P. M. 35.681. The small quantities of methane and butane which are always found respectively in the ethane and propane products for refilling the refrigeration cycles reported do not change the behavior of the refrigerant. However, methane and butanes may be necessary constituents up to a maximum of 3 and 8% molar respectively, depending on the temperature obtainable for the condensation of the refrigerants and the temperature on the border between the two cycles.
I vapori prodotti nei quattro scambiatori sono compressi nel compressore K300, le cui caratteristiche sono: The vapors produced in the four exchangers are compressed in the K300 compressor, whose characteristics are:
Stadio P asp, kPa Potenza, kW mc/h attuali 1 183 11205 197180 2 430 20377 188179 3° 872 37842 160279 4° 1830 40152 110000 Totale 109576 Stage P asp, kPa Power, kW mc / h current 1 183 11205 197180 2 430 20377 188179 3 ° 872 37842 160279 4 ° 1830 40152 110000 Total 109576
Confronto. Comparison.
Le prestazioni del nuovo schema sono state confrontate con i dati di letteratura elaborati da H. Paradowski e P. Hagyard, Comparing five LNG processes, Palladian Publications Ltd 2005. I parametri presi a confronto sono stati la potenza totale dei compressori di processo e le portate volumetriche massime di ciascun compressore, alle condizioni di clima caldo. I cinque processi esaminati dai detti Autori sono: - il C3/MCR, in cui il ciclo primario (utilizzando la stessa terminologia fin qui usata) è a refrigerante misto ed il secondario è un ciclo a propano The performances of the new scheme were compared with the literature data elaborated by H. Paradowski and P. Hagyard, Comparing five LNG processes, Palladian Publications Ltd 2005. The parameters taken in comparison were the total power of the process compressors and the flow rates. maximum volumes of each compressor, under hot climate conditions. The five processes examined by the authors are: - the C3 / MCR, in which the primary cycle (using the same terminology used up to now) is a mixed refrigerant and the secondary is a propane cycle
- il DMR, in cui anche il ciclo secondario è a refrigerante misto - the DMR, in which the secondary cycle is also a mixed refrigerant
- il Liquefin, basato su due cicli a refrigerante misto, in cui il primario ha un solo stadio di refrigerazione-compressione - Liquefin, based on two mixed refrigerant cycles, in which the primary has a single refrigeration-compression stage
- il SMR-SP, con un unico ciclo a refrigerante misto, evaporato a una sola pressione - the SMR-SP, with a single mixed refrigerant cycle, evaporated at a single pressure
- il SMR-DP, con un unico ciclo a refrigerante misto, evaporato a due pressioni Abbiamo preso in esame per il confronto la produzione di GNL in serbatoio, 651 t/h per lo studio e 961 ,3 t/h per l’esempio su riportato. A parità di efficienza politropica dei compressori, 82 %, i valori di potenza e portata dello Studio possono essere riportati alle condizioni dell’Esempio per semplice proporzione. - the SMR-DP, with a single mixed refrigerant cycle, evaporated at two pressures We have taken into consideration for the comparison the production of LNG in the tank, 651 t / h for the study and 961, 3 t / h for the example reported above. With the same polytropic efficiency of the compressors, 82%, the power and flow rate values of the Study can be reported to the conditions of the Example by simple proportion.
Per una produzione di GNL in serbatoio di 961 ,3 t/h (8 milioni di t/anno) si ottiene la seguente tabella: For an LNG tank production of 961.3 t / h (8 million t / year) the following table is obtained:
Processo Potenza, Portata, act. mc/h Portata, act. mc/h kW totali ciclo primario ciclo secondario C3/MCR 234049 344059 299760 DMR 228290 344059 189011 Process Power, Flow, act. mc / h Flow rate, act. mc / h kW total primary cycle secondary cycle C3 / MCR 234049 344059 299760 DMR 228290 344059 189011
LIQUEFIN 229768 231834 268750 LIQUEFIN 229768 231834 268750
SMR-SP 252359 332246 SMR-SP 252359 332246
SMR-DP 247339 286470 162431 SMR-DP 247339 286470 162431
ESEMPIO 225360 177325 197180 EXAMPLE 225360 177325 197180
Per il confronto della portata volumetrica attuale è stato considerata in ogni processo la maggiore delle portate ai compressori, evidenziata in neretto. Risulta per l’Esempio una portata pari al 75 % della portata minore dello Studio. For the comparison of the current volumetric flow rate, the higher of the compressors flow rates, highlighted in bold, were considered in each process. For the example, a range equal to 75% of the lower range of the Study results.
Il processo proposto conserva i vantaggi della tecnica nota. Difatti: The proposed process retains the advantages of the known art. In fact:
- la potenza necessaria ricalca i valori riportati in letteratura - the necessary power follows the values reported in the literature
- la flessibilità è addirittura migliorata perché oltre alla possibilità di variare la temperatura al confine tra i due cicli frigoriferi è ora più facile variare la temperatura tra gli stadi di ogni ciclo frigorifero - flexibility has even improved because in addition to the possibility of varying the temperature on the border between the two refrigeration cycles, it is now easier to vary the temperature between the stages of each refrigeration cycle
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